The invention relates to a glass melting furnace for glazing environmentally hazardous wastes, such as asbestos or demolition material containing asbestos, ashes, filter dusts and the like. The furnace has a melting section and a withdrawal section, and, in operation, a molten glass layer, a molten layer of undissolved sulfates, and a batch layer succeeding one another from the bottom up in the melting section. The withdrawal section is separated from the melting section by a first dividing wall extending downwardly into the furnace interior and terminating at a distance from the furnace floor, a second dividing wall is disposed for the formation of an underside glass passage, and a glass outlet is formed at the outer end of the withdrawal section with an overflow edge. Such a furnace is disclosed in U.S. Pat. No. 3,499,743.
U.S. Pat. No. 4,678,493 discloses an electrical melting furnace for glazing asbestos. The asbestos waste in pulverized and moistened form is fed to this melting furnace to achieve a sufficient melting rate on the one hand, and on the other hand to minimize dispersion of asbestos dust. During its operation, the melting furnace is kept at a pressure below atmospheric to prevent the escape of dust. What is considered disadvantageous in this known melting furnace is especially its high energy demand, because the evaporation of the moisture from the asbestos batch involves the loss of a great amount of thermal energy from the melt. Furthermore, the previous pulverizing of the asbestos waste requires much energy. Operation of the furnace in a partial vacuum is necessary in this case because the evaporation proceeds relatively violently, causing many particles of asbestos to be ejected from the batch. Accordingly, a high-powered blower with a filter system is provided in this known furnace, which signifies additional cost in the construction and operation of the furnace. U.S. Pat. No. 3,499,743 discloses a glass melting furnace in which a first dividing wall extends all the way into the glass layer, so that a free surface is established behind it in normal operation. If undissolved sulfates should nevertheless pass under the first dividing wall, the second dividing wall is provided in the outlet part of the furnace. The undissolved sulfates layer provides for an improved thermal gradient from the glass melt to the incoming batch and thus tends to accelerate the melting. It is a disadvantage of this furnace that the undissolved sulfates layer varies in thickness according to the composition of the input batch. This signifies that a more rational and reliable operation of the furnace is possible only if it is fed with a precisely defined batch of known composition. This requirement can be met in the conventional production of, for example, bottle glass and the like from relatively pure raw materials, but not in the glazing of wastes, since the latter have varying compositions in which at least the proportions are unknown. In the glazing of wastes in these glass melting furnaces it would thus have to be expected that at least from time to time undissolved sulfates will be contained in the glass drawn from the furnace, which makes the glass unsuitable for further processing.
The problem is therefore to create a glass melting furnace of the kind described above, in which wastes of varying composition can be glazed reliably and at low cost.
When demolition material is melted, or waste dumps are removed, however, it can happen that not only damp, but also very wet material is melted.
In this case, accumulations of water can form during storage and transport, and when they are thrown onto the molten sulfate layer floating on the glass bath they can result in explosion-like disturbances.
It is also the purpose of the invention, therefore, to create a glass melting furnace in which the charging of batch material containing free water can be surely prevented by simple means.
Also, the glass melting furnace is to be able easily to process waste materials containing asbestos, and the elimination of the water that must be removed before charging the batch is to be possible without polluting the environment.